Composition for adhering plastic film to a vapor penetrable non-metallic substrate



United States Patent Ofi ice 3,524,828 Patented Aug. 18, 1970 US. Cl. 260--17 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an adhesive composition for applying a plastic film over a vapor penetrable backing or core material comprising an aqueous emulsion consisting essentially of a copolymer containing, for each 100 parts by weight thereof, 60-75 parts of vinyl acetate and the remainder of the copolymer being an alkyl ester of an unsaturated acid and mixtures thereof with methacrylic acid and a water dispersible non-separating combination of (1) a water soluble ester of a mono-C -C alkyl ether of a C C glycol with a C -C saturated monocarboxylic aliphatic acid and (2) a plasticizing ester of glycerin with saturated C -C monocarboxylic aliphatic acid, the ester of the said ether and the plasticizing ester being dispersed in substantially non-separating condition in the aqueous phase of the emulsion.

The invention is particularly useful in the application of vinyl chloride and other plastic films or sheets to a penetrable substrate, e.g., wood, cardboard, fiber board, particle or flake board, paper and woven and knitted fabrics.

In making such products, it is customary to ply the plastic sheeting, with an adhesive coating thereon, to the surface of the core or backing material and then send the assembly through the nip between several pairs of rotated, compressing rollers in series arrangement. To obtain proper adherence of the plastic sheeting to said material during the short time during which pressure is applied has been a problem.

The present invention provides adhesive compositions which develop proper tackiness and bond strength before the adhesive film is completely or even largely dried and solve the problem.

The invention comprises the herein described adhesive in the form of an aqueous emulsion including a resin component that is the copolymer of vinyl acetate and an acrylic ester or mixed homopolymers of each, a special coalescing agent and plasticizer combination, and suitably also a thickener.

More specifically, the resin which gives particularly good results is a copolymer of vinyl acetate with ethyl acrylate in the proportions of about 15-90 parts and ordinarily 60-75 parts of the acetate with sufficient acrylate ester to make 100 parts total weight of copolymer. In place of the acetate component of the copolymer I may use vinyl esters of other lower fatty acids, e.g., propionic and butyric acids or combinations thereof. In place of ethyl acrylate I may use methyl, butyl, octyl, or other C alkyl acrylate or methacrylate. The methacrylate when selected may be in admixture with one or more of the acrylates or a copolymer therewith.

Satisfactory coalescing agents are the appreciably or freely water soluble esters or mixed esters of mono-C alkyl ethers of any glycol having 2-8 carbon atoms to the molecule, examples being the methyl, ethyl, propyl and butyl ethers of ethylene, propylene, butylene glycols and di or other polyglycols thereof, esterified with a C aliphatic saturated acid, namely, acetic, propionic and butyric, or mixtures of said esters, the glycol ether and acid being so selected from the groups stated as to make an ester having substantial solubility in water; an example is the acetate of the monobutyl ether of ethylene glycol (Butyl Cellosolve acetate).

As the plasticizer which, in combination with the glycol ether ester of kind described, promotes the desired grabbing or development of tackiness and strength before the aqueous coating film of the emulsion of the adhesive is completely dried, glycerine triacetate (triacetin) and the tributyrate (tributyrin) illustrate the class that gives the desired results. For some purposes I may use also the monodiand tri-C aliphatic acid esters of glycerin e.g., monoand diacetin; mono-, di-, or tripropionate or butyrate esters of glycerin. The lower members of the series give better overall results. Triacetin and tributyrin, illustrating a suitable range of solubility of the plasticizer, dissolve to the extent of about 7 parts and 0.02 part respectively, in parts of water at 20 C. They are infinitely soluble in dry coalescing agents of the kind described herein.

In general, I select a combination of coalescing agent and plasticizer, from the groups given, as tested by stirring in water alone, so that the combination is water dispersible to an emulsion that is non-separating. There is thus prevented separation of these action solvents for the resin, either by settling or rising of them in the applied adhesive film, either of which, if occurring, would cause layering out of said solvents in excessive concentration on a face of the film, in contact with one of the surfaces to be adhered and thus weaken the adhesive strength at the critical zone of adhesion.

Thickeners which are satisfactory for the present purpose also are water dispersible, examples being alkyl and hydroxyalkyl cellulose as as Natrosol 250 H (hydroxyethyl cellulose), hydroxymethyl cellulose, ethyl hydroxyethyl cellulose, the sodium salt of carboxymethyl cellulose, and the homopolymer of ethylene oxide (polyethylene oxide) of molecular weight 4,000 to 4,000,000, such as Polyox WSR 35, 205, or 301. Polysaccharide gums (cf. Kirk & Othmer, Encyclopedia of Chemical Technology, vol. 11, page 6, 1953) may be used as thickeners, for instance, karaya, locust bean, tragacanth, or guar gum. The thickener used is of kind and in amount to provide suitable rheological properties for application of the adhesive to the substrate.

Proportions of the several components on the dry basis that are permissible and others that are recommended in commercial adhesive formulations are shown in the following table.

Parts by weight for 100 parts copolymer of vinyl ester-acrylic es er Ingredient Permissible Recommended coalescing agent, eg., butyl Cellosolve The viscosity range stated in the table above is for an emulsion of 50% solids, i.e., non-water materials. The viscosity for a given set of proportions will vary in expected manner with concentration of the solids.

The proportion of the thickener to give the viscosities varies with the thickener selected. For the preferred viscosity of 20-40 poises, the amount of Polyox when used is suitably about 0.005 %1% of the weight of the emulsion, the exact amount required being generally inversely proportional to the molecular weight. For the various polysaccharide gums, a suitable proportion is approximately 0.2%1.5% of the emulsion.

As to conditions, I compound the ingredients in any manner usual in this art. Ordinarily, I add a preformed mixture of the coalescing agent and plasticizer to the copolymer latex. a commercial aqueous emulsion containing about 55% solids, and stir the mix until the initial thickening that may occur disappears or until uniformiity results. Then I stir in the thickener which, before its admixture, is suitably either swollen in water or mixed with a portion of said coalescing agent and then with water. Alternatively, the thickener may be slurried in the mixed agent and plasticizer and the slurry then mixed into the latex.

The invention will be further described in connection with the following specific examples or the practice of it, proportions here and elsewhere herein being expressed as parts by weight unless specifically stated to the contrary.

A part of the triacetin and the methyl Cellosolve acetate were premixed and slowly added to the stirred copolymer latex. The resulting blend Was stirred until the initial thickening resulting from the addition of the plasticizer-coalescing agent blend had disappeared and the mix had become smooth. Next introduced was the required amount of Natrosol 250 H which had been previously wet with an equal weight of methyl Cellosolve acetate, i.e., with the remainder thereof, and then dissolved in sufficient water to yield a solution of 3% solids concentration. The whole was then agitated and mixed thoroughly.

The final product was an emulsion that showed no settling in 6 months standing, had a viscosity between 30 and 40 poises, on the average for many batches, pH 4.5-5, and weight per gallon 8.97 lbs. Dried films of the adhesive on glass were clear and water-white.

This emulsion on a cellulosic substrate has shown a gra time (period of developing tack and strength of the adhesive film) of 6090 seconds, the exact time depending on the exact nature of the substrate. The product was non-staining.

The following controls B and C are not part of the invention. They show failure of (1) the coalescing agent with an insoluble plasticizer and (2) a soluble plasticizer with no coalescing agent for the present purpose.

Control B: Dry wt. Copolymer A of Formula A 100 Dioctyl adipate 1 l Methyl Cellosolve acetate 5 Natrosol 250 H, 3% solution 0.75

1 To replace triacetin.

4 Control C: Dry wt. Copolymer A of Formula A 100 Triacetin 10 Ethanol, 95% (several grades used separately) 5 Natrosol 250 H, 3% solution 0.75

1 To replace methyl Cellosolve acetate.

Although Control C also was prepared with the mixing procedure employed for Formula A, the resulting products showed no grab until after seconds.

EXAMPLE II The procedure and composition outlined under Example I, Formula A, were used except that the triacetin therein used was replaced by tributyrin. Also, the methyl Cellosolve acetate used therein was replaced, separately and in turn, by equal amounts of butyl Cellosolve acetate, and butyl Carbitol acetate (acetate of butyl ether of diethylene glycol).

In a modification of this example, the triacetin of Formula A is replaced by an equal weight of a mixture of 50% triacetin and 50% tributyn'n.

EXAMPLE III The procedure and composition of Example I, Formula A are used except that the Natrosol thickener was replaced, separately and in turn, by 0.1 part of Polyox WSR-35 (average M.W. about 200,000), 0.5 part of locust bean gum, 0.5 part of tragacanth and 0.5 part of guar gum, the mixing and other operations being otherwise exactly as described in Example I.

The properties of the products of Examples H-IV are satisfactory.

EXAMPLE IV The adhesive of Example 1, Formula A was applied by reverse roll coater to the underside of a vinyl chloride sheet to a depth wet of about 2 mils in thickness and the thus adhesively coated sheet immediately plied to the surface of sized, compressed paper board. The assembly was then passed through a series of rollers adjusted to a pressure of approximately 20 p.s.i. at the nip, at a speed of about 25 feet per minute. Total time in the nip was of the order of 1-2 seconds. Within about 60 seconds, strength of adhesive had developed, as shown here by the bond of the adhesive being suflicient to cause fibre tear in the substrate under forced delamination from the vinyl chloride sheet.

EXAMPLE V This example provides an adhesive for application to relatively less porous substrates, such as plywood, poplar sheeting or highly compressed Wood-fiber board. In order to obtain good bond strength and adhesive penetration on such substrates, it is necessary to reduce the solids of the adhesive emulsion to approximately 48%50%. If this solids reduction is done with additional water, a retardation of gra results, with the time of grab being ordinarily increased to about 70-120 seconds or more, the exact time depending on film thickness and porosity of the substrate. If, however, the solids reduction is accomplished in part with an organic liquid diluent such as benzene, tetrahydrofurane, or a chlorinated hydrocarbon, e.g., methylene chloride, all of evaporation rate above that of water, very little slowing of grab occurs, grab times of 30-50 seconds duration persisting. Yet the property of penetrating the substrate and developing adequate bond strength remains.

An example of a formulation for such purpose is:

Parts, dry basis The amount of diluent used to replace the water of dilution may vary within the range about -15 parts for 100 parts of said copolymer. Lesser amounts areineifectual and larger amounts defeat the purpose, by reversing the speed up of grab, to an actual slowing down thereof.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

1 claim:

'1. An adhesive emulsion consisting essentially of water, a resin component consisting essentially of, for each 100 parts by weight of the component, a copolymer of 60-75 parts vinyl acetate and correspondingly 4025 parts of a C alkyl ester of an unsaturated acid selected from the group consisting of acrylic acid and mixtures thereof with methacrylic acid and a water-dispersible non-separating combination of (1) a water soluble ester of a mono- C alkyl ether of a C glycol with a C saturated monocarboxylic aliphatic acid and (2) a plasticizing ester of glycerin with saturated C monocarboxylic aliphatic acid, the ester of the said other and the plasticizing ester being dispersed in substantially non-separating condition in the aqueous phase of the emulsion.

2. The adhesive emulsion of claim 1, the ester of said ether being the acetate of the monobutyl ether of ethylene glycol and said plasticizing ester being a glycerin acetate.

3. The adhesive emulsion of claim 1, said plasticizer being triacetin.

4. The adhesive emulsion of claim 1, said plasticizer being tributyrin.

5. The adhesive emulsion of claim 1, the proportions by weight being about 3-15 parts of the ester of said ether and 215 parts of the plasticizing ester for 100 parts of said copolymer.

6. The adhesive emulsion of claim 1 including an admixed thickener in amount to raise the viscosity of the emulsion to about -100 poises at C.

7. The adhesive emulsion of claim 1 including an admixed thickener selected from the group consisting of the water dispersible alkyl and hydroxyalkyl celluloses, sodium salt of carboxymethyl cellulose, polysaccharide gums, and polyoxyethylene of molecular weight within the range 4,000-4,000,000, the proportion of the thickener being that giving to the emulsion a viscosity of about 10-100 poises at 20 C. when the proportion of water in the emulsion is approximately 40% of the total weight thereof.

8. The adhesive emulsion of claim 7, said thickener being hydroxyethyl cellulose.

9. An adhesive emulsion consisting essentially of the following components in proportions by weight approximately as follows: 35-55 parts of water, parts of a vinyl acetate and ethyl-acrylate copolymer, the proportions by weight of each monomer in 100 parts by weight of said copolymer being -75 parts vinyl acetate and correspondingly 40-25 parts of ethyl acrylate, 3-15 parts of the acetate of the monobutyl ether of ethylene glycol, 2-15 parts of tributyrin, and 0005-2 parts of hydroxyethyl cellulose.

10. The adhesive emulsion of claim 7, said thickener being polyoxyethylene of average molecular weight about 200,000.

11. The adhesive emulsion of claim 1, said thickener being guar gum.

12. The adhesive of claim 1, including an admixed emulsified organic liquid diluent, the diluent being of evaporation rate above that of water and in the proportion of about 5-15 parts by weight for parts of said copolymer.

References Cited UNITED STATES PATENTS 3,325,425 6/1967 Bray 260-17 3,258,443 6/ 1966 Cantor et al 260--29.6 2,628,948 4/1950 Kunze et al. 260-17 3,164,562 1/ 1965 Breed 260-17 3,296,169 1/ 1967 Corz 260--29.6

OTHER REFERENCES Industrial Plasticizers, Mellan, The MacMillan Co. (1963).

Buttrey, Plasticizer 1957, p. 46. Cleaver-Hume Press Ltd.

WILLIAM H. SHORT, Primary Examiner E. WOODBERRY, Assistant Examiner US. Cl. X.R. 

